Biosensor detection systems take advantage of the selective interaction and binding (affinity) of certain biological molecules to identify molecular structures and furthermore measure levels of different analytes such as toxins, polymers, hormones, DNA strands, proteins, and bacteria. Affinity-based biosensors exploit selective binding and interaction of certain bio-molecules (recognition probes) to detect specific target analytes in biological samples. The performance of biosensors in terms of signal to noise ratio and dynamic range is generally constrained by the characteristics of the molecular recognition layer which captures the target analytes, and not by the transducer and read-circuitry. An advantage of biosensors is their capability to be implemented in parallel and in an array format. Biosensors in parallel may compensate for limited detection performance. Presently, densely packed biosensor arrays which detect thousands of different analytes simultaneously (microarrays) are popular in Genomics, Proteomics, molecular diagnostics, and systems biology.
The essential role of the biosensor platforms and the parallel and miniaturized versions of them as microarrays are to exploit specific bindings of the probe-target complexes to produce detectable signals, which correlate with the presence of the targets and conceivably their abundance.
Many of the microarrays currently used in biological and medical research are DNA microarrays, in which the probe that is spotted or synthesized onto a solid surface is DNA. However, in addition to nucleic acids, microarray technologies are applicable to other types of biochemical compounds and analytes that can be immobilized on solid surfaces, such as proteins, carbohydrates, and lipids. Microarrays can be used to study the interactions between compounds of a same or different type (for example, protein-protein interactions, or protein-carbohydrate interactions).
Beside all the uncertainties within the measurement results, there is also a question in microarrays and most affinity-based biosensor systems, and that is of the necessary incubation time (hybridization time for DNA microarrays). Since the incubation kinetics in the microarrays experiments is a function of analyte diffusion, reaction chamber size, temperature and binding kinetics of every analyte species, as well as the unknown analyte concentrations, the settling time of the system is quite complex and unpredictable. Although all these questions can, to some extent, be empirically addressed, they are still major impediments in microarray technology and platform-to-platform inconsistencies can be caused by them.
In conventional fluorescent-based microarrays and other extrinsic reporter-based (label-based) biosensors assays, the detection of captured analytes is usually carried out after the incubation step. In some cases, proper fluorescent and reporter intensity measurements are compromised in the presence of a large concentration of floating (unbound) labeled species in the incubation solution, whose signal can overwhelm the target-specific signal from the captured targets. When the incubation is ceased and the solution is removed from the surface of the array, the washing artifacts often occur that make the analysis of the data even more challenging. Thus there exists a need for affinity based sensors that are able to simultaneously obtain high quality measurements of the binding characteristics of multiple analytes, and that are able to determine the amounts of those analytes in solution.
The emerging high-through screening and point-of-care (PoC) diagnostics applications demand the integration of the biochemical part (assays) of the detection platform with the transducer and the detection circuitry. A microarray is desired in the art that offers compact and cost-efficient solutions with a high production yield and robust functionality.